Cyanate ester resins, developed during the 1980s, join epoxy resins and bismaleimide resins as the third major class of thermosetting resins. Polycyanurates or cross-linked cyanate resins are prepared by the cyclopolymerization of aromatic cyanate esters. These cyanate esters are bisphenol derivatives containing a plurality of cyanate functional groups. When heated, the cyanate functionality undergoes exothermic trimerization to form substituted triazine rings. Subsequent curing produces the thermosetting resin.
Cyanate esters are currently employed in rapidly curing adhesive compositions used to bond semiconductor devices or chips, also known as dice, to carrier substrates. Such adhesive compositions include, in addition to the cyanate ester, thermally and/or electrically conductive filler, alkylphenol (as a proton donor participating in the cyclotrimerization cure of the cyanate ester monomer), and a curing catalyst dissolved in the alkylphenol.
Cyanate ester adhesive compositions have eliminated many of the deficiencies inherent in epoxy adhesives and polyimide adhesives, such as low glass transition temperature, high degree of ionic contamination, retention of solvent and lengthy cure. Nevertheless, there still remains room for improvement of die attach pastes containing electrically conductive filler and polycyanate ester monomer in a variety of ways, e.g., in reducing the cost of preparation, as well as the ease of preparation, by avoiding the use of potentially detrimental components (e.g., alkylphenols are acidic species, which are potentially corrosive), by avoiding the use of volatile components (which upon cure tend to bleed out, which may lead to the creation of voids in the cured resin), and the like.